EGGS OF BIRDS. 619 



build nests, but the habit is most perfectly developed among Birds. 

 As is well known, each species has its own peculiar style of nest, and 

 builds it of special materials. Generally the nest is solitary, hidden in 

 some private nook. The perfection of art which is reached by some 

 birds in the making of their nests is marvellous ; they use their bills and 

 their feet, and smooth the inside by twisting round and round. Usually 

 the hen does most of the work, but her mate sometimes helps, both in 

 building the nests and in hatching the young. 



The nest is a cradle rather than a house, for its chief use is to secure 

 an approximately constant warmth for the young which are being 

 formed within the eggs, and to afford protection for the helpless 

 fledglings. At the same time, the nest secures the comfort of the 

 parent-bird during the days and nights of brooding. 



The variety of nests may be illustrated by mentioning the burrowed 

 nests of sand-martins and kingfishers, the ground-nests of game-birds 

 and gulls, the mud-nests of house-swallow and flamingo, the holes 

 which the woodpecker fashions in the tree-stem, the platforms built by 

 doves and eagles, storks and cranes, the basket-nests of most singing- 

 birds, the structures delicately woven by the goldfinch, bullfinch, and 

 humming-birds, the sewed nest of the tailor-bird, the mossy nests of 

 the wrens, the edible nest of the Collocalia, which is chiefly composed 

 of mucin secreted by the salivary glands. 



Eggs of Birds. — When the nest is finished, the eggs are ready to 

 be laid. After they are laid, the patience of brooding begins. With 

 the great care that Birds take of their young we may associate the 

 comparatively small number of the eggs ; but there are probably other 

 reasons why the number of offspring decreases as animals become more 

 highly evolved. 



The size of the egg usually bears some relation to the size of the bird. 

 Of European birds, the swans have the largest eggs, the golden-crested 

 wrens the smallest. It is said that the egg of the extinct Moa some- 

 times measured 9 in. in breadth and 12 in. in length ; while that 

 of the extinct ALpyornis held over two gallons, some six times as 

 much as an ostrich's egg, or a hundred and fifty times as much as 

 a fowl's. Yet the size of the egg is only generally proportional to that 

 of the bird ; for, while the cuckoo is much larger than the lark, the eggs 

 of the two are about the same size ; and while the guillemot and the 

 raven are almost of equal size, the eggs of the former are in volume 

 about ten times larger than those of the latter. The eggs of birds 

 whose young are rapidly hatched and soon leave the nests are large. 

 Professor Newton remarks that " the number of eggs to be covered at 

 one time seems also to have some relation to their size," while from 

 what one notices in' the poultry-yard, and from a comparison of the 

 habits of different birds, it seems probable that a highly nutritive, 

 sluggish bird will have larger eggs than a bird of more active habit and 

 sparser diet. 



The shell of the egg is often very beautifully coloured ; there is a 

 predominant tint upon which are spots, streaks, and blotches of varied 

 colour and disposition, so that the egg is almost always characteristic of 

 the species. The colouring matter consists of pigments related to those 

 of the blood and the bile, and is deposited while the shell is being 



